A President has to be a preacher of sorts, instructing, consoling, summoning citizens to sacrifice for some common good. But candidates are competitors, which means they seldom manage to talk about faith in a way that doesn't disturb people, doesn't divide them, doesn't nail campaign posters on the gates of heaven. Republicans have been charged with exploiting religious voters, Democrats with ignoring them: Hillary Clinton's voice gets tight as she recalls the mocking response she received when she first spoke in spiritual terms about the longing that people felt to invest in causes larger than self-interest. "I talked about my faith...